Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$33.45	13.238%	$37.8781	$37.88	$37.90	$37.90
Purchase #2	$223.37	3.871%	$232.0167	$232.02	$232.00	$232.00
Purchase #3	$104.77	8.308%	$113.4743	$113.47	$113.45	$113.50
Purchase #4	$56.28	4.329%	$58.7164	$58.72	$58.70	$58.70
Purchase #5	$89.74	12.176%	$100.6667	$100.67	$100.65	$100.70
Purchase #6	$127.80	12.556%	$143.8466	$143.85	$143.85	$143.80
Purchase #7	$90.86	11.349%	$101.1717	$101.17	$101.15	$101.20
7 purchase totals =	$726.27		$787.7705	$787.78	$787.70	$787.80